Description: This project seeks to define spatio-temporal relationships between head mesoderm, neural crest, and CNS tissue in the developing mouse, using MRI microscopic techniques. The cranial neural crest of the mouse shows non-uniformities in its migration that may depend on segmental differences in the neural tube from which it originates and/or the environment through which it migrates. Studies from several laboratories have defined genes that are expressed in a non-uniform fashion, suggestive of a role in the segmentation of the cranial mesoderm, neural crest and CNS. However, little is known about the exact spatial or temporal relationships of these genes and developmental events. The proposal lists three specific aims. MRI microscopy "atlases" of mouse craniofacial development will be acquired (aim 1). These digital three-dimensional (3D) atlases will be obtained with MRI microscopy of craniofacial structure precursors in the developing mouse, both in vivo and after fixation. A subset of the animals imaged will be processed by conventional histology and the three image data sets compared. Vital dye fate-mapping of mouse craniofacial development will be done (aim 2). Current MRI contrast agents, especially ones based on Gd-DTPA- dextran and Gd-tagged lipid, will be refined so that small groups of cells can be indelibly marked. After characterizing new agents in fixed specimens, these MRI dyes will be used to follow directly cell and tissue movements within the mouse embryo by repeated MR imaging of the same animal as embryogenesis proceeds. Parallel studies will employ light microscopy (both laser confocal and conventional histological methods) to fate map selected regions and correlate the movements of the cells with molecular domains defined by the expression of lacZ transgenes or by in situ hybridization. MRI microscopy of developmental gene expression will be further developed by synthesis of targeted MRI contrast agents applied to determine patterns of gene expression (aim 3). Three dimensional images of gene expression domains will be compared with developmental events in normal and mutant mice. These experiments are expected to better define spatiotemporal relationships between developmental events such as tissue movements and causal gene expression patterns.